Effectiveness is influenced by capacity of unit. If you are trying to mount a 270 cfm fan more than 30" above cooktop, then it may make noise but will do little to clear the air. If it is 1000 cfm, then it can be higher than 30". So the answer is "it depends". Most people don't mount them more than 36" above the cooktop unless it is a really high powered unit.

Hello Abhinaya, Siemens & Bosch make are better ones.. Thanks Amit Cornerstone Designs Bangalore

Jt Kr, Either the technician is making a weird suggestion or you may have misunderstood his suggestion. If the Chimney is installed 360 mm away from the wall the entire hob unit projects out by 360 MM. It would technically make it difficult for any taller person to cook. As it will be brushing against their heads. The suction may be impacted. What he may be suggesting instead (please recheck) is that don't mount it on the wall rather some models can be installed on the ceiling. He may be referring to that installation on the beam. (Such models are called island hobs) If you have the floor plan and 2 D elevation measurements we can try recommending alternatives. Thanks Nitin Cornerstone Designs, Bangalore.

Hi Mr Shivam above said brands are any ways very popular in market  and have good collection,  also try QUTON , they also have some good collection, but don't get confused with so many brands in mind,